Storm Surge

Characteristics

Storm surge is an abnormal rise in water generated by a storm. This is over and above the predicted astronomical tide. Storm surge is sometimes confused with storm tide. Storm tide is defined as the water level rise due to the combination of storm surge and astronomical tide (thus it is an accumulative level).

Storm surge can cause significant flooding particularly when it occurs in relation to normal high tide.

Dangers

Along the coast, storm surge is often the greatest threat to life and property from a hurricane. In the past, large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall.

Hurricane Katrina in 2005 is a prime example of the damage and devastation that can be caused by surge. At least 1500 persons lost their lives during Katrina and many of those deaths occurred directly, or indirectly, as a result of storm surge.

Storm Development

Storm surge is produced when water is pushed toward the shore by the forces of winds moving cyclonically around a storm. The impacts of low barometric pressures are minimal on surge when compared to the wind driven forces. The maximal storm surge for any given area is complex as it can be affected by:

Angle of approach

Central pressures

Forward speed

Radius of maximum winds

Shape and characteristics of coastline features

Slight changes in storm intensity

A shallow slope has the potential for a great more intense storm surge to develop than sharp steep slope. Storm surge will inundate coastal floodplains by dune over wash, tidal elevation rise in inland bays and backwater flooding through coastal river mouths.

Occurrence

The storm surge arrives ahead of the storm center's actual landfall and the more intense the storm is, the sooner the surge arrives. Water rise can be very rapid, posing a serious threat to those who have not yet evacuated flood‐prone areas.

The surge is always highest in the right‐front quadrant of the direction in which the storm is moving. As the storm approaches shore, the greatest storm surge will be to the north of the low‐pressure system or hurricane eye. Such a surge of high water topped by driven by hurricane force winds can be devastating to coastal regions, causing severe beach erosion and property damage along the immediate shoreline.